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%# mffm Time Code
%# Time Code for multimedia systems
%#
%# Copyright (C) 2000, 2001 Matt R. Flax <flatmax@ieee.org>
%#
%# This library is free software; you can redistribute it and/or
%# modify it under the terms of the GNU Lesser General Public
%# License as published by the Free Software Foundation; either
%# version 2.1 of the License, or (at your option) any later version.
%#
%# This library is distributed in the hope that it will be useful,
%# but WITHOUT ANY WARRANTY; without even the implied warranty of
%# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
%# Lesser General Public License for more details.
%#
%# You have received a copy of the GNU Lesser General Public License
%# along with this library.
function [a,b]=BPDesign(k,cf,Q3dB,fs)
%# deisgns a BP filter centred at cf and of width Q3dB with gain k
%# For the purpose of neural systems, it is probably best to have as
%# little ripple in the pass band as possible.
%#
%# input : k = gain at the freq. peak of the filter
%# cf = Center frreq. (Hz)
%# Q3dB = cf/(high3dB-low3dB)
%# fs = sample freq.
%#
%# output: a = denominator of the discrete transfer function (poles)
%# b = numerator of the discrete transfer function (zeros)
BW=cf/Q3dB
lowFreq=(cf-BW/2)*2/fs %# normalised
highFreq=(cf+BW/2)*2/fs %# normalised
n=2;
[b, a] = butter(n, [lowFreq, highFreq]);
b*=k; %# scale by the gain
endfunction
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